Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Flow and return valves OFF
ENSURE APPLIANCE IS COMPLETELY DISCHARGED AND DRAINED

Measurement:

Inspect auto bypass valve for free operation, damage and blockage.
The appliance has an inbuilt automatic adjustable bypass valve.
The pressure can be adjusted between approximately 170 and 350 mbar.
Approximately 250 is preset (mid position).
Should the bypass require resetting refer to the manufactures instructions.